The present invention relates to an improvement on an interlocking railing construction of the type disclosed in U.S. Pat. No. 3,498,589. More particularly, the present invention relates to a method of interlocking a lateral bar material and the end of a hollow post and the construction of the joint used to interlock said members.
Tubular railings made of aluminum by extrusion molding have recently gained wide use as stairway, balcony and enclosure handrails. The popularity of such railings stems from their good appearance, that fact that they do not require painting, the simplicity with which they can be assembled and the low cost at which they can be mass produced. In general, railings of this type are not assembled by bolt-nut jointing or welding but instead by insertion of wedges used to interlock separate members. Therefore, the railings can be assembled even by unskilled persons with the aid of only a hammer.
The interlocking force exerted by a wedge is greatly influenced by variations in size which are unavoidable with mass-produced parts. The influence of size variations is slight where the wedges are inserted until the insertion forces of the wedges become a predetermined constant value. Variations in force arise, however, in the interlocking of the rails and the hollow posts because the wedges must be inserted by a constant depth (and not until a certain force is produced) and the size of the wedges as well as the other parts is not uniform. Therefore, when a relatively small wedge is by chance inserted into a post having a relatively large center hole the force interlocking the members is corresponding small. As the joint is likely to weaken even further with the passage of time, the railing may well become a hazard to human life.
Accordingly, a first object of the present invention is to provide a simple and reliable method of fixing the joint portion between a lateral member such as a handrail and one end of a hollow post without using wedges, welding or bolts and nuts and further to provide a joint portion which uses a self-tapping screw as the fixing means both when the lateral member is mounted to pass over or under the hollow post and when the lateral member is fixed to the top or bottom of the post by one end thereof.